1. Field of the Invention
The present invention relates to a magnetic interface circuit used for a modular jack connected between a network cable and a circuit board.
2. Description of Related Art
U.S. Pat. No. 7,123,117, issued to Chen et al. on Oct. 17, 2006, discloses a magnetic interface circuit for interfacing between a cable side and a circuit side of a networking communication channel. The magnetic interface circuit has two transmit channels each including a transformer and a 3-wire common mode choke (CMC) connected with each other. The transformer has a first winding connected to the cable side of the channel and a second winding connected to the circuit side of the channel. Each of the first and second windings has two output ports. The 3-wire CMC has a middle or center winding and two outer windings. The outer windings are respectively connected to the output ports of the first or second winding. The center winding has an end connected with a center tap of the transformer and another end connected with a power supply (V+). High frequency noise transmitted through the two outer windings could be coupled to the center winding and reflected back between the center tap of the transformer and the center winding of the 3-wire CMC, affecting filtering performance (common mode noise reduction). Moreover, the noise of a power supply could also reflect back between the center tap of the transformer and the center winding of the 3-wire CMC. A modular jack having such magnetic interface circuit could be easily made through a slight circuit change on an inner printed circuit board of an existing modular jack, such as disclosed in U.S. Pat. No. 7,708,595.
A magnetic interface circuit having improved filtering performance is desired.